GB 1 199 831 A discloses a roof ventilation unit, in which two shutters, when in the closed state, form a cover for a fan. The shutters are hinged outside a tube in which the fan lies, in order to reduce the formation of turbulence in the air flow when the shutters are in the open state.
When the shutters are in the closed state, they close the air passage opening, and when the shutters are in the open state the fan is not protected against the ingress of water. Furthermore, the shutters and the fan are fastened on a roof and are not intended to be mounted on a switchgear cabinet.
DE 92 12 876 U1 describes a fan for connection to a space containing water droplets, having a fan housing with an axial air inlet and an outlet on the circumferential side, and a fan wheel arranged in the fan housing with a shaft and a shaft feed-through on the opposite side from the air inlet. The housing has a wall projection, which is for example shaped conically, surrounding the shaft feed-through on the housing side.
No measures are taken to prevent ingress of liquid into the fan housing; rather, this ingress is tolerated.
DE 196 36 500 C2 discloses a seal insert for electrical insulation equipment, which comprises a hollow cylindrical casing and a collar formed at a right angle thereon. At its outer edge, the collar is provided with a coaming, on the end of which an outwardly facing circumferential projection is formed which engages in the edge region of a cover frame, so as to prevent the ingress of moisture or water.
This arrangement can prevent only lateral but not frontal ingress of water, since the cover is configured as a frame. The installation equipment is furthermore provided for under-surface fitting and not for mounting in a switchgear cabinet.
Switchgear cabinets of the type mentioned in the introduction are known from the prior art and are used in wind turbines, for example to accommodate electronic components for controlling pitch drives, so that these switchgear cabinets are also referred to as pitch switchgear cabinets. In wind turbines, climate control of pitch switchgear cabinets is problematic when, with high ambient temperatures in the vicinity, high powers and therefore also high power losses occur in the switchgear cabinets since thermal dissipation through the switchgear cabinet surface is often insufficient by itself.
Although it would be possible to use heat exchangers in order to comply with the protection class, for reasons of space and costs this is generally not feasible. It is possible to use standard filter fans as an alternative, although they only achieve the required protection classes when the switchgear cabinet has a defined position so that no water can enter through slats or slits of the filter fan. This defined position is however not provided by pitch switchgear cabinets since they are arranged in the rotor or in the rotor hub of the wind turbine, and are subjected to a constant position change owing to the rotation of the rotor. The slats arranged on the outer side of commercially available filter fans point downwards in the normal fitting position, so that the air inlet opening of the fan is covered against water jets from above. When used in the rotor of a wind turbine, however, the filter fan also passes through positions in which the slats point upwards and therefore readily permit entry of water. In this context, a not inconsiderable amount of water is to be envisaged in the rotor hub (for example condensed water from the rotor blades).